Sample card transport method for biological sample testing machine

ABSTRACT

A sample card transport station moves a test sample card from an incubation station for the card to a transmittance and fluorescence optical station in a sample testing machine. The sample card transport station has a drive belt and an associated stepper motor. The belt supports the card from one side of the card. A ledge having a card slot is disposed above the belt. The card is snugly received within the card slot, and supported from below by the drive belt and rollers for the belt. When the motor turns the belt, the belt grips the card and slides the card along the slot to the optical stations, without any slippage between the belt and the card. This construction provides for precise control over the movement of the card.

BACKGROUND OF THE INVENTION

A. Field of the Invention

This invention relates to the field of optical systems that conductanalysis of biological test samples, and the mechanical systems thatplace the test samples into position for reading by the optical system.These systems are typically found in automated microbiology, immunoassayand biological sample testing machines, and related diagnostic oranalytical machines such as found in infectious disease,immuno-chemistry and nucleic acid probe systems.

B. Description of Related Art

It is known in the art that biological samples can be subject to opticalanalysis using various techniques, two of which are transmittance andfluorescence optical analysis. The purpose of the analysis may be toidentify an unknown biological agent in the sample, test the sample todetermine the concentration of a substance in the sample, or determinewhether the biological agent is susceptible to various antibiotics. Theanalysis may further identify the concentration of antibiotic that wouldbe effective in treating an infection containing the agent.

A technique has been developed for conducting optical analysis ofbiological samples that involves the use of a sealed test sample cardcontaining a plurality of small sample wells or reaction sites. Duringmanufacture of the cards, e.g., for microbiological analysis of testsamples, the sample wells are loaded with growth media for differentbiological agents, or else various concentrations of differentantibiotics. Fluid containing the biological sample enters the card viaan L-shaped transfer tube extending outwardly from a transfer tube portin the card. An internal fluid passageway structure allows the fluid tomigrate from the transfer tube port to the wells of the card.

To load the card with fluid, the transfer tube is placed in a test tubecontaining a biological sample, and the card/transfer tube/test tubeassembly is placed in a vacuum filling and sealing machine, such as theVitek® Filler Sealer (from bioMerieux Vitek, Inc.). The filling andsealing machine generates a vacuum, the release of which causes thefluid in the test tube to be drawn into the wells of the sample card.

After the wells of the card are loaded with the sample, the transfertube is cut off and melted, sealing the interior of the card, and thecard is placed into a reading and incubation machine. The reading andincubating machine incubates the cards at a desired temperature. Anoptical reader is provided for conducting transmittance testing of thewells of the card. Basically, the cards are stacked in columns in thereading machine, and an optical system moves up and down the column ofcards, pulling the cards into the transmittance optics one at a time,reading the cards, and placing the cards back in the column of cards.The Vitek® reading machine is described generally in the Charles et al.,U.S. Pat. No. 4,188,280.

The ability of the optical reading system to take accurate reads of thesample wells is a function of several variables, such as the presence ofair bubbles in the sample wells, the accurate placement of the growth orantibiotic medium in the sample wells, the number of reads obtainedduring the incubation of the cards, and the sophistication of the opticsof the reading machine. Obviously, to improve the analyticalcapabilities of the machine, the performance of the optical readingsystem is critical.

In addition to the Charles et at. patent mentioned above, prior artpatents relating to the general subject of optical systems for analysisof biological samples include U.S. Pat. No. 4,626,684 to Landa, and U.S.Pat. No. 5,340,747 to Eden. Other background references include U.S.Pat. No. 4,477,190; WIPO published patent application WO 84/00609(Heller); and U.S. Pat. No. 5,372,783 to Lackie. The patent to Robinsonet al., U.S. Pat. No. 5,374,395, discloses a diagnostic instrument inwhich a carousel holds test packs during incubation periods and rotatesthe test packs past an optical reader that senses the presence of ananalyte in the sample. Prior art systems for transporting specimencarriers in diagnostic machines include the above-referenced Charles etal. patent, U.S. Pat. No. 5,417,922 to Markin et at; U.S. Pat. No.4,236,825 to Gilford et al., and the above-referenced Robinson et at.patent.

An object of the invention is to provide an optical reading system forreading test sample cards that enables a rapid and preciseidentification and analysis of the specimens. The invention incorporatesa unique fluorescence-based detection substation and an advancedmultiwavelength transmittance testing substation, enabling both types ofanalysis to be performed automatically for the cards.

The fluorescence substation achieves a significant throughput bysimultaneously analyzing multiple sample wells using a singlefluorescence light source and multiple detector elements in a singleassembly. Reliability, compactness, and repeatability in thefluorescence measurements are much improved over prior art systems.

Furthermore, prior art multiple channel fluorometers typically use asingle light source that is split into multiple channels using opticalfibers, which direct the light through sample wells onto a singlemultiplexer detector or separate individual detectors. These systemstend to be large and complex assemblies requiting precise positioning ofoptical fibers. In addition, energy and signal losses in the opticalfibers reduce the efficiency of the system. The present system performstrue simultaneous readings of multiple sample wells using a singleexcitation source and multiple emission detection devices without theneed for separate optical fibers or excitation and emission pathways.The fluorescence substation further includes a lamp reference detector,enabling precise readings of the wells of the card independent of anychanges in the output of the excitation light source.

The inventive fluorescence substation also includes an optical shuttleassembly and solid reference source that allows for automaticcalibration of the photodiode detectors when the cards are not beingread. To calibrate the system, the shuttle moves the solid referenceinto the optical path. The solid reference is illuminated by the lamp,and emits radiation at the wavelength of the fluorophores. The radiationis received by the photodetectors, and the outputs can be calibrated byadjusting moveable gain amplifiers, insuring accurate measurements offluorescence from the wells of the card.

The present invention also provides for a sample card transport systemfor precisely moving the test sample card relative to the optical systemso as to permit numerous data sets in each reading cycle. The samplecard transport system moves the cards from an incubation chamber to thetransmittance and/or fluorescence optics substations, where readings aretaken of the card. At the transmittance substation, multiple reads ofthe wells are taken at several positions across the well, generating alarge number of data sets. Once the test is complete, the sample cardtransport system moves the card to a card output tray. If more testingis needed, the card is moved back to the carousel. The precise movementfeatures of the present test sample card transport system are believedto be unique.

These and other objects, advantages and features of the invention willbecome more apparent from the following detailed description ofpresently preferred embodiments of the invention.

SUMMARY OF THE INVENTION

In one aspect of the invention, a transport system is provided formoving a test sample card having a plurality of sample wells and firstand second edges relative to an optical system for reading the samplewells. The transport system has a support bulkhead for supporting theoptical system and a ledge mounted to the bulkhead for maintainingalignment of the card relative to the optical system. The ledge definesa card slot for receiving the first edge of the card, the slot defininga card travel direction. A drive subassembly is mounted to the supportbulkhead, and includes:

a) a drive belt supported by at least one roller and movable relative tothe ledge in a direction parallel to the card travel direction, thedrive belt engaging the second edge of the card to move the cardrelative to the optical system;

b) means for driving the belt; and

c) spring means for biasing the drive subassembly towards the ledge soas to maintain pressure between the card, the ledge means and the belt.

The drive belt slides the card relative to the ledge in the card traveldirection without significant slippage between the drive belt and thesecond edge of the card, thereby permitting the motor to move the cardrelative to the optical system with substantial precision.

The substantial precision in moving the card relative to the opticalsystem is particularly taken advantage of in transmission opticalanalysis of the wells of the card. The presence of air bubbles in thesample well can prevent accurate reading of the sample wells, since theair bubble creates a zone in the well that is nearly opaque, allowinglittle of the transmittance illumination in that zone to impinge on thedetector. This problem is overcome by causing the motor and drive beltto move the card in a plurality of discrete steps in the forward or thereverse direction across the width of the well, so as to enable aplurality of transmittance measurements at different locations of thewells in the card. For example, the card may be moved into fourteendifferent positions relative to the source and detector, and thetransmittance source flashed rapidly at 10 flashes per position,resulting in 140 data points for each well. Simple statistical analysisof the data can detect the presence of an air pocket in the well, butenough data is obtained from the other portions of the well outside ofthe air pocket to permit adequate transmission measurement.

The optical reading system further includes a fluorescence opticalstation. The wells of the card are loaded with a fluorophore duringmanufacture that is released or inhibited by biological or chemicalprocesses once the wells are loaded with biological samples. Thefluorophores are excitable upon the receipt of radiation at a lightexcitation wavelength and emit radiation at a light emission wavelength.A preferred fluorescence station comprises:

(a) an excitation lamp for simultaneously illuminating the column ofwells with an excitation light at the excitation wavelength;

(b) a dichromatic beam splitter reflecting a portion of the excitationlight from the excitation lamp simultaneously to the column of wells,the beam splitter at least partially transparent to radiation at theemission wavelength;

(c) a reference detector receiving excitation light passing from theexcitation lamp through the beam splitter;

(d) a reflector assembly disposed opposite the wells from the excitationlamp and beam splitter for reflecting excitation light passing throughthe wells back into the wells;

(e) a plurality of detectors, one for each of the sample wells, thedetectors receiving radiation at the emission energy level transmittedfrom the sample wells through the beam splitter; and

(f) a peak detector circuit for comparing the output of the referencedetector and the plurality of detectors. The inclusion of the referencedetector and a beam splitter at least partially transmissive toexcitation radiation enables a ratio of detector output to referenceoutput to be calculated in the station electronics. This ratio ofsignals provides for consistent measurements of fluorescence from thewells, independent of a change in output of the excitation lamp overtime.

In a preferred form of the invention, the excitation light passes fromthe beam splitter to the well and reflection assembly along the sameoptical path. The reflection assembly further comprises an opticalshuttle having a solid reference source that emits radiation at theemission energy level of the fluorophore. The optical shuttle moves thereference source into the optical path. When the solid reference sourceis positioned in the optical path and operated to emit radiation, asimple calibration of the detectors may be made such that they allproduce the same signal for a given output from the reference source asthey did at an initial calibration with a control reference. A preferredsolid reference source is a phosphorescent material (such as Europium)that emits radiation at the same wavelength as the fluorophores in thewell when it is illuminated by the excitation lamp.

These and many other features and advantages of the invention will bemore apparent from the following detailed description of preferredembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Presently preferred embodiments of the invention are depicted in thedrawings, wherein like reference numerals refer to like elements in thevarious views, and wherein:

FIG. 1 is a perspective view of a preferred automatic biological sampletesting machine that incorporates the optical reading and sample cardtransport systems of the invention;

FIG. 2 is a perspective view of the machine of FIG. 1, with the dilutingand pipetting stations removed to better illustrate the vacuum stationof the machine;

FIG. 3 is a plan view of a preferred sample card transport system forthe machine of FIGS. 1 and 2;

FIG. 4 is a side view of the sample card transport station of FIG. 3,looking in the direction of the carousel and incubation station of FIGS.1 and 2;

FIG. 5 is a sectional view of the carriage and slide assembly of FIGS. 3and 4, which permits the drive subassembly to move relative to thebulkhead;

FIG. 6A is a plan view of the left-hand edge of the drive subassembly ofFIG. 3 and 4, showing the ejecting of the card from the drivesubassembly into a card reject tray;

FIG. 6B is a perspective view of a push mechanism that pushes the cardsout of the slots in the carousel of FIG. 2 into the sample cardtransport system of FIG. 3;

FIG. 6C is a perspective view of the push mechanism as seen from therear of the bulkhead;

FIG. 7 is a perspective view of the fluorescence optical substation ofthe optical reading system of FIGS. 1 and 2, with the reflector assemblyin an open position to better illustrate the optical head;

FIG. 7A is a plan view of the front of the reflector assembly of FIG. 7;

FIG. 7B is a plan view of the rear of the reflector assembly of FIG. 7;

FIG. 7C is a side view of the reflector assembly of FIG. 7;

FIG. 8 is a sectional view of the fluorescence optical substation ofFIG. 7;

FIG. 9 is an exploded view of the flashlamp cassette of FIG. 7;

FIG. 10 is a front view of the optical head of FIG. 7, showing theoptical interrupt channel and the six channels for reading six wells ofthe card;

FIG. 11 is a rear view of the optical head of FIG. 7;

FIG. 12A is a top view of the lens assembly holder of FIG. 7;

FIG. 12B is a rear view of the lens assembly holder;

FIG. 12C is a side view of the lens assembly holder;

FIG. 12D is an end view of the lens assembly holder;

FIG. 13A is a rear view of the optical interface block of FIG. 7,showing the detector board mounted to the optical interface block;

FIG. 13B is a front view of the optical interface block of FIG. 13A,showing the placement of the bandpass filters in front of the opticalchannels;

FIG. 14A is a front view of the detector board of FIG. 8, showing thephotodiode detectors that are placed behind the six channels of theoptical interface block of FIG. 13;

FIG. 14B is a rear view of the detector board of FIG. 14A;

FIG. 15 is a block diagram of a preferred peak detector board for thefluorescence substation of FIG. 15;

FIG. 16 is a cross section of the solid standard of FIG. 8;

FIG. 17 is a graph of the excitation and emission spectra of the solidstandard of FIG. 16;

FIG. 18 is a graph of the responsivity as a function of incidentradiation wavelength of the photodiode detectors of FIG. 14A;

FIG. 19 is a schematic diagram showing the relationship of the flashlamp of FIG. 9 and the optical channels of the optical head of FIG. 8;

FIG. 20 is a graph of the filter transmittance as a function ofwavelength for the 445 nM bandpass filter of FIG. 8;

FIG. 21 is a graph of the reflectance (and transmittance) as a functionof wavelength for the beam splitter of FIG. 8;

FIG. 22 is a graph of the filter transmittance as a function ofwavelength for the 365 nM bandpass filter of FIG. 8;

FIG. 23 is a graph of the reflectance as a function of wavelength forthe UV cold mirror of FIG. 8;

FIG. 24 is a detailed elevational view of the transmittance substationof FIG. 3;

FIG. 25 is a perspective view of one of the three LED transmittanceemission sources of FIG. 24; and

FIG. 26 is a sectional view of the transmittance substation of FIG. 24,showing the relationship between the LED transmittance light source,sample well, and photodiode detector;

FIG. 27 is an elevational view of the sample well and LED output for thetransmittance substation of FIG. 24.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Overview of Preferred Sample Testing Machine

FIG. 1 is a perspective view of a preferred biological sample testingmachine 20. The following detailed description of the preferredembodiment of the inventive optical reader and sample card transportsystems will be discussed in the context of the biological sampletesting machine 20. It will be appreciated, however, that the principlesof the invention may be used in other types of testing machines besidesthe preferred microbiological sample testing machine 20. Other possibleimplementations include chemical testing, immunochemistry, immunoassay,and nucleic probe assay machines.

The biological sample testing machine 20 includes a test samplepositioning system 100, consisting of four independent motor-drivenpaddles, which is designed to slide a sample tray 22 (referred to hereinas a "boat") across a base pan 24 around the machine 20 to severaldiscrete stations, where various operations are performed on the samplesin the boat 22. Prior to the start of the procedure, a technician loadsa cassette 26 with a plurality of test cards 28 and receptacles such astest tubes 30 containing biological samples to be tested. Each test card28 has an L-shaped transfer tube 32 protruding therefrom for permittingfluids containing the biological samples to be drawn from the test tubes30 into the wells of the test cards 28. The technician places the loadedcassette 26 into the boat 22 at a loading station for the machine, suchas the front, right hand corner of the base pan 24 shown in FIG. 1. Thecombined boat 22 and loaded cassette 26 are then moved as a unit overthe surface of the base pan 24 about the machine 22 by the test samplepositioning system 100.

In a typical microbiological testing scenario, described below forpurposes of illustration but not limitation, the test cards 28 come intwo varieties: (1) identification cards, in which particular differentgrowth media are placed in the wells of the card 28 when the cards aremanufactured, and (2) susceptibility cards, in which differentconcentrations of different antibiotics are placed in the wells of thecard 28. The identification cards are used to identify the particularunknown biological agent present in the sample. The susceptibility cardsare used to determine the susceptibility of the biological agent tovarious concentrations of antibiotics or other drugs. In the testprocedure described below, identification and susceptibility tests canbe performed on a single sample in one cycle of operation of the machine20. To accomplish this, the cassette 26 is loaded such that a test tube30A containing a biological or control sample, connected via a transfertube 32 to an identification card 28A, is placed adjacent to a test tube30B connected via a transfer tube 32 to a susceptibility card 28B.

The cards 28 preferably contain or may have affixed bar codes across thetop of the card for reading by a bar code reader built into the machine20. The bar codes are unique to each card, and identify cardinformation, such as card type, expiration date, serial number, and areused to correlate test data from the cards with the patient and thebiological sample. In addition, the entire boat or cassette may havesample information for all of the cards loaded in the cassette stored ona memory device affixed to the cassette 26, such as a memory button or"touch button" available from Dallas Semiconductor Corp., 4401 S.Beltwood Parkway, Dallas Tex.

In the representative example shown in FIG. 1, seven or eight of thetest tubes 30 in the boat 22 contain biological samples, and are influid communication with identification cards 28 by the straw-liketransfer tube 32. The biological sample test tube 30A and its associatedidentification card 28A can be thought of as a set. The biologicalsample test tubes and identification cards are typically arranged in analternating pattern in the cassette 26. Each biological sample test tube30A and identification card 28A set is adjacent to an empty test tube30B placed in communication with a susceptibility card 28B via atransfer tube 32. It will be appreciated that the cards and associatedtest tubes could be ordered in any order in the cassette 26 depending onthe particular testing requirements for the samples. For example, thecards could be arranged as follows: identification (ID), susceptibility(SU), ID, ID, ID, SU, SU, ID, SU . . . . Further examples would be allidentification cards and all susceptibility cards.

The test sample positioning system 100 operates to move the boat 22 andcassette 26 over the base pan 24 first to a diluting station 200. Thediluting station contains a rotating shot tube 202, by which apredetermined volume of diluent (such as saline solution) is added tothe empty susceptibility test tubes in the cassette 26, e.g. test tube30B. As the leading edge of the boat 22 is moved to the left during thisprocess, it passes under a pipetting station 300. The pipetting station300 includes a mechanism that automatically removes a pipette 302 from asource of pipettes 304, lowers the pipette 302 into the biologicalsample test tube 30A, and removes with vacuum a predetermined volume ofbiological fluid from the biological sample test tube 30A using thepipette 302.

The test sample positioning system 100 then moves the boat 22 to theleft by an amount equal to the separation distance between adjacent testtubes 30A and 30B, e.g. 15 mm. The pipetting station 300 then lowers thepipette 302 containing the biological fluid from the biological sampletest tube 30A into the adjacent susceptibility test tube 30B (havingalready received a quantity of diluent from the diluting station 200),expels the fluid into the test tube 30B, and drops the pipette 302 intothe susceptibility test tube 30B. The process of movement of the boat 22by the test sample positioning system 100, adding diluent to thesusceptibility test tubes 30B at the diluting station 200, andtransferring of biological samples from the biological sample test tubes30A to the adjacent susceptibility test tubes 30B at the pipettingstation 300, continues until all of the identification andsusceptibility test tubes sets (if any) in the boat 22 have been soprocessed. By virtue of the close spacing of the pipetting station 300and the diluting station 200, simultaneous diluting and pipettingoperations can be performed on multiple test tubes in a single boat 22.After the last pipetting operation has been performed, the test samplepositioning system 100 then moves the boat all the way to the left-handedge of the base pan 24.

It will be understood by persons skilled in the art that the cassette 26may be loaded entirely with biological samples in the test tubes 30 andidentification cards 28, such as the case where a batch of biologicalsamples are to be tested to identify the contents of the samples. Inthis example, the diluting and pipetting operations are not necessary.However, in other types of sample testing, other diluents or fluids maybe added to or withdrawn from the test tubes. In the example of where nodiluting or pipetting operations are performed, the cassette 26 isloaded with test tubes and cards, and the positioning system 100 wouldsimply move the boat 22 and loaded cassette 26 directly past thediluting station 200 and the pipetting station 300 without stopping, allthe way to the left hand edge of the base pan 24.

Once at the left hand edge of the base pan 24, the test samplepositioning system 100 operates to move the boat 22 along the left handedge to a vacuum station 400. The vacuum station 400 is seen better inFIG. 2, which is a perspective view of the machine 22 with the dilutingstation 200 and the pipetting station 300 removed. At the vacuum station400, a vacuum chamber 402 is lowered onto the boat 22 such that thebottom surface of the vacuum chamber 402 sealingly engages the topperipheral surface 23 of the boat 22. Vacuum is applied to the chamber402 under microprocessor control, causing air in the interior of thetest sample cards 28 to evacuate out of their associated test tubes andto be withdrawn from the chamber 402. The vacuum cycle is preciselymanaged to optimize filling using a closed loop servo system to regulatethe change of vacuum and timing of the complete cycle. After apredetermined period, the chamber 402 is vented to atmosphere undermicroprocessor control. The venting of the cards causes the fluid in thetest tubes 30 to be drawn into the cards 28, filling the wells in thecards 28.

The test sample positioning system 100 then operates to advance the boat22 to the fight across the rear of the base pan 24 to a cut and sealstation 500, located behind the center mount 34 in FIGS. 1 and 2. Thecut and seal station 500 consists of a hot cutting wire and attachedsupport plate (not shown), and a drive mechanism 502 that lowers thecutting wire and support plate to the same elevation as the top portionof the transfer tubes 32 adjacent to where the transfer tubes 32 enterthe test cards 28. As the boat 22 is advanced past the cut and sealstation 500, the transfer tubes 32 are forced past the hot cutting wire.With the assistance of fore and aft constraints placed on the movementof the cards 28 by the walls of the cassette 26, and the lateralconstraints on the movement of the card 28 by the cassette and wallstructures of the machine 20, the hot cutting wire cuts the transfertubes 32 by melting of the transfer tube material as the boat 22 isadvanced past the hot cutting wire. A small stub of transfer tubematerial is left on the exterior of the card 28. The stub seals theinterior of the card 28 from the atmosphere.

The test sample positioning system 100 then advances the boat 22 acrossthe rear of the base pan 24 behind the center mount 34 to a carouselincubation station 600. A reciprocating cam driver is mounted to thecenter mount 34 opposite a slot 602 in the machine that pushes the cardsoff the cassette 26 one at a time through the slot 602 into a carousel604. The carousel 604 is housed in an enclosure that is maintained at anincubation temperature of, for example, 35 degrees C. The enclosure isnot shown in FIGS. 1 and 2 in order to show the carousel 604. Thecarousel 604 is rotated in synchronism with the movement of the boat 22over the rear of the base pan 26 by the test sample positioning system100, so as to place the next slot in the carousel 604 in line with theslot 602 opposite the next card in the cassette 26. If the carousel isonly going to be partially loaded with cards, it may be advisable toload the cards into every other slot or two periodically in order tobalance out the weight distribution in the carousel 604. For example,where the carousel has 60 slots and only 30 cards are to be processed,the cards are loaded into every other slot.

After all of the cards 28 have been loaded into the slots of thecarousel 604, the boat 22 is advanced along the right hand edge of thebase pan 24 back to its starting position (shown in FIGS. 1 and 2) forremoval of the cassette 26 (containing the test tubes and transfer tubesremnants) and receipt of a new cassette.

As the cards 28 are being incubated in the incubation station 600, thecards are periodically, sequentially pushed out of the slots of thecarousel 604 at the top of the carousel 604, one at a time, and moved byan optical scanner transport station 700 past a fluorescence andtransmittance optics station 800. The wells of the card 28 areselectively subject to transmittance and fluorescence optical testing bythe transmittance and fluorescence optics station 800. The transmittanceand fluorescence optics station 800 includes detectors and processingcircuitry to generate transmittance and fluorescence data for the wellsin the cards 28, and to report the data to a central processing unit forthe machine 22. If the test is not complete, the transport station 700moves the card 28 back into its slot in the carousel 604 for moreincubation and additional reading.

Generally, any given well in the card is subjected to eitherfluorescence testing or transmittance testing. A particular card 28 mayhave wells that requiring transmittance testing, and other wells thatrequire fluorescence testing, hence the card is moved to bothfluorescence substation and to transmittance substation. Other cards mayrequire only transmittance testing, or fluorescence testing, and thuswould be moved by the transport station 700 to the proper opticalsubstation.

Typically, each card will be read every 15 minutes as the carousel makesone revolution. Typical incubation times for the cards 28 are on theorder of two to eighteen hours, consisting of roughly four transmittanceand fluorescence data sets per hour for each of the wells in the card 28subject to the optical analysis.

After the testing is complete, the cards are moved by the opticalscanner transport system 700 into a card output station 900 shown inFIG. 2. The card output station 900 consists of a detachable tray 902that is placed to the side of the optical station 800 at approximatelythe same elevation as the optical station 800. The technician removesthe tray 902 from the machine 20 as needed or when the tray 902 is fullof cards, empties the cards into a suitable biohazard disposal unit, andreplaces the tray 902 back into the machine 20.

Sample Card Transport Station 700

Referring now to FIG. 3, the sample card transport station 700 is shownin a plan view. The station 700 includes a drive assembly 702 having acover plate 704 which is mounted to a bulkhead or support 706. Theoptical reader system 800 in the preferred embodiment consists of atransmittance substation 802 and a fluorescence substation 804, whichare mounted to the bulkhead 706. The sample card 28 is moved from thecarousel 604 by the drive assembly 702 through the optical reader system800 and back to the carousel 604 if the card 28 needs further incubationand additional reading. If the card has been sufficiently incubatedbased on the analysis of data from the optical reader system 800, thecard 28 is moved to a card reject tray to the left of the optical system800.

The drive assembly 702 consists of a stepper motor 708, shown in dashedlines, positioned behind a mounting bracket 709. The motor 708 drives atiming pulley 711 that moves an endless, substantially inelastic, drivebelt 710 having teeth 710 over a series of rollers 712. The belt 710 issupported at the top of the cover plate 704 by a set of rollers 712. Thepath of the belt through the rollers 712 is shown in dashed lines inFIG. 3. It can be seen that the belt 710 passes across the top of thecover plate 704 and through the optical substations 802 and 804. Thedrive belt 710 engages the bottom edge of the card 28 along the top ofthe cover plate 704. A suitable drive belt 710 can be obtained from theGates Rubber Co., of Denver, Colo.

A ledge 718 mounted to the bulkhead 706 is provided above the belt 710and the optical reading system 800. The ledge has a slot 720 whichreceives the upper edge of the card 28. The ledge 718 and slot 720defines a card travel direction. When the card 28 is pushed out of thecarousel 604, the card 28 is snugly positioned in the space between theslot 720 and the belt 710. The entire drive assembly 702, includingcover plate 704, stepper motor 708 and drive belt 710, is movablerelative to the support bulkhead 706. To permit the relative movement, aset of carriage and slide assemblies 716 are provided, one of which isshown in more detail in FIGS. 4 and 5. As seen in FIG. 5, each of thecarriage and slide assemblies 716 includes a slide 730 mounted to thebulkhead 706 by a bolt 734. The carriage 726 is mounted to the coverplate 704 by a set of four screws 724. The carriage 726 slides relativeto the slide member 730 by means of ball bearings 728 which slide alonga groove 732. In the preferred embodiment, two of the carriage and slideassemblies 716 are provided, one on each side of the cover plate 704.

The entire drive assembly 702 is biased upwards towards the ledge 718 bybiasing springs 714. The springs have a top end 713 engaging a pin 714Amounted to the bulkhead 706, and a bottom end 715 engaging a pin 714Bmounted to the cover plate 704. Three springs 714 in all are preferred,and are placed at the center and sides of the cover plate 704. Thesprings 714 each have a spring constant K of 16.5 lbs/in., for a totalof 49.5 lbs/in for the three springs. Small slots are provided in thecover plate to allow for movement of the pins 714A, B. The purpose ofthe springs 714 is to constantly maintain the proper upward pressure onthe card 28 by the belt 710, such as in the case of some tolerancevariation in the height of the cards. The drive belt 710 must provideenough upward force so as to permit the belt to engage the bottom of thecard 28 and move the card along the slot, but not too much to causebinding by the drive motor or too little force, which would cause thebelt to slip relative to the bottom of the card. By maintaining theproper upward force on the card, such that belt travel is directlytranslated into card travel, precise movement by the stepper motor 708results is precise movement of the card 28 relative to the opticalsystem 800. This precise movement is discussed in greater detail inconjunction with the operation of the transmittance substation 802.

Referring to FIG. 4, the drive assembly 702 and bulkhead 706 are shownin a side view, looking towards the carousel 604 and incubation station600 of FIGS. 2 and 3. The rollers 712 at the top of the cover plate 704form a slot, as shown, which helps support the bottom edge of the card28. The card 28 is snugly positioned between the belt 710 and the slot720 in the ledge 718. The upward force on the card 28 by the springs 714causes the belt 710 to grip the bottom edge of the card 28, such thatthe card 28 is slid along the ledge 718 by the drive belt 710 withoutany slippage between the belt 710 and the card 28. To facilitate thesliding motion, the slot 720 (FIG. 3) is made from a low frictionmaterial such as Delrin or given a low friction coating. The bottom edgeof the card 28 is provided with a knurled texture surface (e.g., smallparallel raised ridges oriented perpendicular to the direction of cardtravel) to better enable the belt 710 to grip the card 28 as the belt710 moves backward and forwards over the rollers 712. The top edge ofthe card 28 is smooth.

Referring again to FIG. 3, in order to place the card into the samplecard transport system 700, a push mechanism is provided to push the card28 out of the carousel 604. The push mechanism is shown in FIGS. 6B and6C. FIG. 6B is a perspective view of the carousel 604 showing the pushmechanism 648 mounted to the front of the carousel bulkhead 652, andFIG. 6C shows the mechanism 648 as seen from the rear of the bulkhead652. The push mechanism includes an alignment block 654 mounted to thebulkhead 652 and a driver 656 that reciprocates back and forth relativeto the block 654. A motor 648 having a gear 662 is mounted behind thebulkhead 652. The teeth of the gear 662 cooperate with a set of teeth658 on the driver 656, such that rotation of the gear 662 backwards andforwards causes the driver 658 to move in the direction shown by thearrow 664 (FIG. 6C) in the space between a lower slot 666 and an upperslot 668 in the block 654. The end of the driver 656 is positioned inalignment with the top slot 614 in the carousel 604. When the driver 656is operated by the motor 648 such that the driver 656 is pushed into theslot 614, the card 28 within the slot 614 is pushed out of the slot intothe space between the ledge 718 and the drive belt 710. (Theconstruction and operation of the reciprocating cam mechanism that loadsthe cards 28 into the carousel from the cassette 26 is essentially thesame as that for the push mechanism 648). An optical detector 650 isprovided directly above the slot 614 so as to control the rotation ofthe carousel 604 such that slot 614 is properly positioned adjacent thedriver 656 and ledge 718.

The push assembly 648 slides the card 28 out of the slot 614 at the topof the carousel 604 and places the card 28 at the extreme right handedge of the drive assembly 702 adjacent to the extreme upper fight driveroller 712A. The stepper motor 708 is operated in a forward direction(rotating the timing pulling 711 in a counter-clockwise direction),causing the drive belt 710 to move to the left and move the card 28 tothe left towards the transmittance substation 802.

When the leading edge of the card 28 reaches the transmittancesubstation 802, an optical interrupt LED in the transmittance substationtransmits radiation through an optical interrupt aperture 112 at thebase of the card 28. An optical interrupt detector senses the radiationand sends a signal to the control system to cause the motor 708 to stop.When the motor 708 stops, the first column of wells 110 in the card 28are positioned directly opposite a set of eight transmittance LEDs inthe transmittance substation 804, which conduct transmittance testing ofthe column of wells in the card 28.

After an initial illumination of the LEDs, the motor 708 is operated torapidly move the belt 710 in a series of small steps, such that thetransmittance optics illuminates the individual wells at a series ofpositions across the width of the wells. This precise movement of thecards 28 achieves a large set of data for the wells 110. Thetransmittance testing at multiple positions across the wells 110 willlikely include a detection of any air pockets or debris, if any, in thewells, enabling the data processing system to detect and possibly rejectan abnormal transmittance measurement.

Where fluorescence testing is called for, after all of the wells of thecard 28 have been subject to the transmittance testing by transmittancesubstation 802, the motor 708 and belt 710 slide the card 28 to thefluorescence substation 804, wherein fluorescence testing of the wells110 takes place. Depending on the test status, the card 28 is theneither returned to the carousel 604 by moving the motor 708 and belt 710in the reverse direction, or else the motor 708 and belt 710 areoperated to move the card all the way to the left hand edge of the driveassembly 702 to place the card 28 in a card disposal mechanism.

Referring now to FIGS. 3, 4, and 6A, the card disposal mechanism 900 hasa tray 902 in which the cards are stacked as they exit the sample cardtransport system 700. The ledge 718 is provided with a slant portion 719at the extreme left-hand end of the ledge 718. When the card 28 is movedpast the end of the cover plate 704 onto the tray 902, the upper righthand shoulder 114 of the card 28 is placed into contact with the slantportion 719. The tray 902 is slightly lower than the elevation of thebelt 710 at the top of the cover plate 704, assisting the placement ofthe upper shoulder 114 against the slant 719. A resultant force F (FIG.6A) is imparted to the card 28 by the drive belt 710 and slant portion719, causing the card 28 to snap out of the drive assembly 702 into thecard reject tray 902.

Fluorescence Optics Substation 804

Referring now to FIG. 7, the fluorescence optics substation 804 is shownin a perspective view isolated from the machine 20. The substation 804includes a selective reflector assembly 806 mounted via a hinge 808 toan optical head 810. The optical head 810 has a plurality of surfaceapertures 812 defining six optical channels between a fluorescenceillumination source and the middle six wells in a column of wells 100 inthe card 28. The placement and number of the optical channels depends onthe lamp size (or number) and the geometry of the sample wells in thecard 28. The illumination source is placed within a flashlamp cassette816. An LED and detector cooperate with the optical interrupt aperture112 along the base of the card 28 to precisely position the card in thespace between the front surface apertures and the reflector assembly.

When the hinge 808 is in a closed condition, the selective reflectorassembly 806 is positioned parallel to the apertures 812. The card 28 ismoved back and forth in the space defined by the front surface apertures812 and the reflector assembly 806.

The selective reflector assembly 806 has a stepper motor 801 which movesan optical shuttle 803 back and forth. A reflector 852 and a solidreference 850 are mounted to the optical shuttle 803. The purpose of thereflector and solid reference are described in more detail below.

Referring to FIG. 7A, the front of the selective reflector assembly 806is shown isolated from the rest of the station 804 in a plan view. Theoptical shuttle 803 travels back and forth along a pair of guides 807Aand 807B. In normal operation, the shuttle 803 is in a position suchthat the reflector 852 is placed directly opposite the apertures 812 ofthe optical head 810. Whenever a calibration of the detectors in theoptical head 810 is performed, the motor 801 moves the shuttle 803 suchthat the solid reference 850 is placed in the optical path opposite theapertures 812. The selective reflector assembly housing includes ahousing for an LED for the optical interrupt aperture 112 for the card28. A spring clamp 805 is provided to secure the selective reflectorassembly to the head 110 when the assembly 806 is in a closed condition.

FIG. 7B shows the rear of the selective reflector assembly 806. Theselective reflector assembly 806 is shown in a side view in FIG. 7C.Behind the shuttle 803, a well 1000 is provided for a shaft (not shown)from the stepper motor 801. The stepper motor shaft passes through thegap 1002 in the well and is secured to a piece 809 extending upwardlyfrom the rear surface of the optical shuttle 803. A cover plate (notshown) covers the well 1000 by mounting to the screw holes 1001. Theback and forth motion of the shaft of the stepper motor 801 causes theshuttle 803 to slide back and forth along the guides 807A and 807B.

Referring again to FIG. 7, the removeable flash lamp cassette 816 holdsan elongate xenon linear flash lamp, which serves as a fluorescenceillumination source for the fluorophores placed in the wells 110 of thecard 28. The flash lamp cassette 816 is connected to a high voltagepower supply 820. The flashlamp 824 has a high current capacityconnection allowing field replacement of the lamp. This is unique forthis lamp type due to the high pulse currents generated during the flash(over 350 amps).

A peak detector 814 and electronics module is mounted behind the opticalhead 810. The flash lamp cassette 816 includes a interface block 854 anda lamp holder 856 which are shown in further detail in FIG. 9.

Referring now to FIG. 8, the fluorescence optics substation 804 is shownin a sectional view perpendicular to the axis of the flash lamp 824 andthe six photodiode detectors. The flash lamp cassette 816 houses thexenon lamp 824, which is mounted at the focus of an elongate cylindricalparabolic reflecting mirror 822. The flash lamp radiation R is reflectedoff of a cold mirror 826 onto a 365 nM filter 828, which filters theradiation R to pass radiation at the excitation wavelength of thefluorophores. After passing through the filter 828, the radiation Rreflects off a dichromatic beam splitter 830 along its optical path 833and out of the apertures 812 and into the card wells 110. Any radiationpassing through the wells 110 is reflected off the reflector 852 in theselective reflector assembly 806 and reflected back into the wells 110.The radiation excites the fluorophores in the well 110, causing thefluorophore to briefly to emit radiation. The emission radiation isshown as a dashed line in FIG. 8. The emission radiation passes throughthe dichromatic beam splitter 830, through a focusing lens 836 and bandpass filter 838 onto a photodiode detector 840. There are six photodiodedetectors in all for the six optical channels.

The use of a selective reflector 852 enhances the signal-to-noise ratioand minimizes optical cross-talk by doubling the optical path. Further,when the card 28 is positioned for reading by the fluorescence stationby means of the optical interrupt, the wells in the card are oriented topromote optical separation of the wells to minimize optical cross-talkand maximize the fluorescence signal. The card 28 material is preferablyopaque to minimize cross-talk, and white to maximize the fluorescencesignal.

The dichromatic beam splitter 830 is highly reflective to radiation atthe excitation wavelength of the fluorophores, reflecting approximately95% of the radiation into the well 110. However, the dichromatic beamsplitter 830 is highly transmissive to radiation at the emissionwavelength of the fluorophores, passing most of the radiation from thefluorophore along the same optical path 833 onto the detectors 840.

Approximately 5% of the radiation from the lamp 824 that is notreflected off the dichromatic beam splitter 830 is transmitted along anoptical path 834 to a mirror 832. The mirror 832 reflects the radiationthrough a focusing lens 836A and a band pass filter 846 to a referencephotodiode detector 844. The reference detector 844 is used by the peakdetector circuit 814 to compute the ratio of the signal detected by thedetectors 840 divided by the signal detected by reference detector 844.The output of the lamp 824 may vary over time, however the ratio of theoutput of the channel detector 840 divided by the output of thereference detector 844 remains constant, i.e., independent of changes inlamp output over time. In addition to compensating for changes in lampintensity, the reference channel 844 can also be used to determine ifthe lamp 824 is providing sufficient light for proper operation of thefluorescence optical system. By monitoring the lamp output at thereference detector 844, the system can automatically determine when thelamp 824 needs to be changed.

Still referring to FIG. 8, the reflector assembly 806 also includes asolid reference 850 which emits radiation at the fluorophore emissionwavelength when the reference 850 is moved into the optical path 833.The construction of a preferred sold reference is shown in FIG. 16.Preferably, the solid reference 850 is a phosphorescent Europium sourcesandwiched between glass plates 853 and having a 450 nM filter placedover the front surface of the glass.

Referring to FIG. 17, the typical excitation and emission of Europium isshown as a function of wavelength. Note from the excitation curve 895that Europium responds to excitation radiation between 200 and about 375nM. Thus, Europium excites at the wavelength that illuminates thefluorophores in the wells 110, i.e., about 365 nM. The Europium emissionspectra 896 has a peak between about 455 and 460 nM, which substantiallyoverlaps with the emission wavelength of the fluorophores in the wells110 card 28. Thus, when the solid reference 850 is placed in the opticalpath 833 and the flash lamp 824 is flashed, the solid reference 850emits radiation at an emission wavelength similar to that of thefluorophores in the wells 110 of the card 28. The solid reference 850 isthus used to compensate calibration of the output of the detectors 840,as described below.

It will be appreciated that other kinds of solid references could beused besides the Europium solid reference of FIG. 16. The choice ofemission wavelength depends on the type of fluorophore that is used inthe wells.

Referring now to FIG. 9, the flash lamp cassette 816 is shown in anexploded view. The flash lamp cassette 816 includes a lamp holder 856which receives the parabolic reflector 822 for the flash lamp 824. Theflash lamp 824 is mounted in a pair of adjustment pieces 858 and securedin place by mounting screws 864. The adjustment pieces 858 receive apair adjustment springs 860 and adjustment screws 862. The adjustmentscrews 862 pass through apertures in the interface block 854 and seat inthe adjustment pieces 858. By loosening and tightening the adjustmentscrews 862, the tilt of the flash lamp 824 relative to the cylindricalparabolic reflector 822 is adjusted so as to make the long axis of thelamp 824 lie at the focus of the cylindrical parabolic reflector 822.The interface block 854 includes an aperture 857 for allowing radiationfrom the flash lamp 824 to pass out of the interface block 854 and offthe cold mirror 826 (FIG. 8) and towards the dichromatic beam splitter830 and sample wells 110.

The optical head 810 is shown in FIGS. 10 and 11. FIG. 10 is a plan viewof the face of the optical head 810 as seen from the card 28 as itpasses the fluorescence substation 804. The head 810 includes a headplate 866 within which the apertures 812 and an optical interruptaperture 811 are positioned. A photodetector is placed behind theoptical interrupt aperture and is used in combination with the opticalinterrupt aperture 112 of the card 28 to determine when the card 28 isprecisely positioned within the fluorescence substation 804. Referringnow to FIG. 11, the rear of the head plate 866 is shown. The cold mirror826 and dichromatic beam splitter 830 are placed within the optical headplate 866 and extend lengthwise across a set of six channels 837positioned parallel in alignment with the middle six wells of a columnof wells in the card 28.

Referring now to FIGS. 12A-12D, the lenses 836 and 836A of FIG. 8 areheld by a lens holder piece 848. The lens holder 848 is shown in topplan view in FIG. 12A, a bottom plan view in FIG. 12B, a side view inFIG. 12C, and an end view in FIG. 12D. The lens holder 848 includes apeak portion 849 which fits behind the dichromatic beam splitter 830(see FIGS. 8 and 11). The lenses 836 are placed at the base of curvedwalls 839, which cooperate with the channels 837 of FIG. 11 to form anoptical pathway between the lenses 836 and the detectors 840 and 844.The walls 839 prevent crosstalk between adjacent channels by blockinglight from adjacent channels.

The relationship of the flash lamp 824 to the six optical channels isshown in FIG. 19. The flash lamp 824 is of sufficient length such thatthe space between the anode and cathode of the lamp 824 is greater thanor equal to the distance between the six apertures 812 in the opticalhead. FIG. 19 also shows the relative placement of the optical interrupt811 and the reference channel 874 relative to the six apertures 812. Theflash lamp 824 has a trigger wire 825 wrapped around the surface of thelamp 824 that causes the lamp to flash. A suitable flash lamp 824 can beobtained from ILC Technology Inc. of Sunnyvale Calif., part no. L7752.

Referring now to FIGS. 13A and 13B, the fluorescence optical system 804includes an optical interface block 868 which mounts behind the opticalhead 810 and the lens holder 848. The optical interface block 868 has anopen region 870 to allow radiation from the lamp 824 (FIG. 8) to passthrough the block 868 and off the cold mirror 826. The rear of the block868 is shown in FIG. 13A, and includes six channels or passages 872 forthe radiation from the six wells in the card, and a reference channel orpassage 874 for the radiation 834 from the lamp 824 (see FIG. 8). Thephotodiode detector board 842 mounts on the rear of the block 868, asshown in dashed lines in FIG. 13A. Referring to FIG. 13B, the front ofthe block 868 includes a set of mounting pins 878 to mount the lensholder 848 to the block 868. The 445 nM bandpass filter 838 of FIG. 8 issecured in the block 868, as is the 365 nM bandpass filter 846 for thereference channel 874.

Referring now to FIG. 14A, the photodiode detector board 842 is shown ina plan view. The six photodiode detectors 840 are placed directly overthe six channels 872 when the board 842 is mounted to the rear of theblock 868 as shown in FIG. 8 and 13A. An optical interrupt detector 882is provided to detect when light from an optical interrupt LED passesthrough the optical interrupt aperture 112 of the card 48, indicatingproper alignment of the card 28 in the fluorescence substation 804.

Referring to FIG. 14B, the backside of the detector board 842 hasconventional circuit traces 880 that receive the output of thephotodiode detectors 840 and 844 and passes the signals to the peakdetector 814 electronics.

Referring now to FIG. 15, the peak detector 814 of FIG. 7 is shown in ablock diagram form. On the right-hand side of the illustration, the sixoptical channels CH1, CH2, CH3, CH4, CH5, CH6 represent the inputs fromthe six photodiode detectors. These signals are input into a set of sixdetectors and fixed gain amplifiers 844 that convert the current fromthe photodiode to a voltage signal. The reference channel input signalis supplied to a detector and amplifier 884A. The output of thedetectors and fixed gain amplifiers are input into a set of variablegain amplifiers 886. Similarly, the output of the detector amplifier884A is input to a variable gain amplifier 886A. The variable gainamplifiers 886 and 886A supply an output signal to a set of electronicpeak detectors 888.

The peak detectors 888 are all basically the same as the peak detectordescribed in the standard textbook, The Art of Electronics, by Horowitzand Hill, at page 218, FIG. 4.40, which is incorporated by referenceherein. The standard circuit is modified slightly in that atransconductance amplifier is used as the first stage amplifier, insteadof a standard operational amplifier. This device is a voltage-in,current-out amplifier that allows the circuit 888 to operate very fastwith a minimum of signal distortion.

The output of the peak detectors 888 is buffered by a buffer amplifierand supplied to a multichannel input Analog to Digital (A-D) converter890. The output of the peak detector 888A from the reference channel issimilarly buffered and supplied to a reference input 892 in the A-Dconverter 890. A data bus 894 is provided which sends the output of theA-D converter 890 to a microprocessor-based controller board (not shown)which conducts the processing of the signals from the six channels andthe reference photodetector. In particular, the controller board takesthe ratio of the output of the six channels CH1 to CH6 divided by theoutput of the reference channel, to thereby compute a relativefluorescence measurements which is independent of the output of the lamp824.

Once the card 28 is positioned in the fluorescence substation, the lamp824 is flashed at a 25 Hz rate a number of times, such as ten times.After each flash, the A-D converter 890 computes the ratio of eachchannel to the reference and the controller board reads the results.After 10 flashes, the results are averaged for each channel. Thisprocess in conducted in parallel for each of the six channels.

The data bus 894 also supplies control signals to the peak detectors 888and the variable gain amplifiers 886. In the calibration of thedetectors, the controller board adjusts the variable gain amplifiers 886so as to provide an output signal for each channel that matches theoutput signal when an initial calibration of the detectors was made. Forexample, at the time of the installation of the machine, the channelsare calibrated with a card having wells filled with a control solution,and an initial reading of the detectors is stored in a memory.

The response curve for the detectors 840 is shown in FIG. 18. Theresponse curve 897 has a typical spectral response (A/W) of between 0.2and 0.35 in the 400 to 500 nM region of interest. The characteristics ofthe 445 nM pass filter 838 (FIG. 8) are shown in FIG. 20. Thetransmittance curve 828 has a maximum of 50% transmittance at 445 nM.The transmittance curve drops 828 off sharply below 440 nM and higherthan 450 nM, preventing stray radiation from impinging on the photodiodedetectors 840.

The reflectance specifications of the dichromatic beam splitter 830 ofFIG. 8 is shown in FIG. 21. The reflectance curve 899 shows areflectance of 95% and a transmittance of 5% at the flashlamp outputwavelength of 365nM. The reflectance curve drops sharply above 380 nM toa low of about 6.5% reflectance and 93.5% transmittance at the emissionfrequency of the fluorophores, about 445-450 nM. Thus, it can be seenfrom FIG. 21 that the dichromatic beam splitter 830 is highly reflectiveto excitation radiation from the flash lamp 824, but highly transmissiveto emission radiation from the fluorophore in the card wells 110 and thesolid reference 850.

Transmittance Substation 802

Referring now to FIG. 24, a preferred transmittance substation 802 isshown in an elevational view. The substation 802 has three transmittanceoptical sources 770A, 770B and 770C, each of which comprise 8 LEDsources and an optical interrupt LED source. The optical sources 770A-Care separated from each other by a separation distance D equal to theseparation distance between the columns of wells 110 in the card 28.Three sources 770A-C are provided so as to enable transmittance testingat three different wavelengths. The source 770A is shown in perspectiveview in FIG. 25, and has eight LEDS 797 which are separated from eachother by a distance L equal to the distance between adjacent wells 110in the column direction of the card 28. The optical interrupt LED 789shines light throughout the optical interrupt 112 along the base of thecard 28. A set of three columns of transmittance detectors are placedbehind the three sources 770A-C to collect radiation from the LEDs 797and 789 and supply transmission data to the controller board in awell-known manner.

Referring now to FIG. 26, the transmittance source 770A and itsassociated detector 791 are shown in a sectional view in FIG. 26, takenalong the lines 26--26 in FIG. 24. The LED source 797 is mounted to asubstrate 798 in a well known manner and transmits light through theaperture 793 to the sample well 110. The radiation falls on thephotodiode detector 791, which is also mounted to a substrate 792 in awell known manner. The detector 791 is mounted in a housing 795 thatextends vertically directly opposite the detector 770A. The constructionof light source 770A and detector 795 is the same for the other twosources and detectors in the transmittance station 802.

FIG. 27 is an enlarged, elevational view of the sample well 110, showingthe pattern of transmittance radiation 790 that illuminates the well110. Note that the illumination pattern 790 is only a fraction of theentire width of the well 110.

To perform transmittance analysis of the entire well 110, the card 28 ismoved in a series of small increments relative to the source 770A, forexample in 10 or 14 positions, and multiple illuminations of the well110 are taken at each position. A presently preferred transmittanceillumination test set is fourteen equidistant positions across theentire width of the well 110, and 10 illumination events at each of thefourteen positions. This test cab be performed at up to three differenttransmittance wavelengths for every well, resulting in a large set oftransmittance data.

Referring to FIG. 25, as the card 28 is moved out of the carousel 604,the first column 110' in the card is moved to the source 770C havingLEDs of a first wavelength, whereby the 14 movement steps and 10illumination events per step are performed. The card 28 is then advancedsuch that column 110' is positioned opposite the source 770B having LEDsof a second wavelength. The source 770B illuminates the first column110' while the source 770C illuminates the second column. The card 28 isthen moved such that the column 110' is positioned opposite the source770A having LEDs of a third wavelength, and now sources 770A-C alloperate in concert to illuminate three columns of the wellssimultaneously. The card 28 is advanced to the left such that allcolumns are subject to transmittance illumination at the three sets ofwavelengths. A column of LEDS could contain up to eight differentwavelengths in one column if desired. When the last column has beenilluminated by source 770A, the card 28 is moved to the fluorescencesubstation 804 for fluorescence testing, if necessary.

Of course, the operation of the transport system 700 and transmittancesubstation 802 could be controlled such that the card 28 is movedthroughout the station 802 from left to right instead of right to left.Further, a lesser or even greater number of transmittance sources 770could be used if desired.

A preferred test sample card is described in pending application Ser.No. 08/455,534, filed May 31, 1995, which is incorporated by referenceherein.

Presently preferred and alternative embodiments of the invention havebeen described above. Persons of skill in the art will recognize thatmany variation from the preferred embodiments in terms of mechanical,electrical or optical details may be made without departure from thetrue spirit and scope of the invention. This true sprint and scope isdefined by the appended claims, to be interpreted in light of theforegoing.

We claim:
 1. A method for transporting a sample card having first andsecond edges from an incubation station to a reading station in a sampletesting machine, comprising the steps of:placing said sample card in asnug space defined by (1) a slot in an elongated ledge, said slotreceiving said first edge of said card and defining a card traveldirection from said incubation to said reading stations, and (2) a drivebelt positioned parallel to said slot and supporting said second edge ofsaid card, said slot and said drive belt being in vertical alignmentwith said sample card; biasing said drive belt towards said ledge so asto maintain pressure between said drive belt, said card and said slot;and moving said drive belt in said card travel direction so as to slidesaid card through said slot to said reading station without substantialslippage of said card relative to said belt, permitting precise movementof said card relative to said reading station.
 2. The method of claim 1,wherein said card includes at least one column of sample wells, and saidreading station comprises a transmittance optical station; andwhereinthe method further comprises the step of moving said drive belt in aplurality of discrete steps so as to move said column of sample wellspast said transmittance optical station in a plurality of discretepositions, said transmittance optical station operative to take at leastone transmittance measurement of said column of sample wells at each ofsaid discrete steps.
 3. The method of claim 1, wherein said readingstation comprises a fluorescence optical station and wherein the methodfurther comprises the step of:moving said drive belt in a firstdirection so as to move said card to said fluorescence optical stationand moving said drive belt in a second direction opposite to said firstdirection so as to move said card from said fluorescence optical stationback to said incubation station.
 4. The method of claim 1, wherein saidincubation station comprises a carousel and wherein said sample card ismoved from said carousel to said reading station.